Generics programming in Swift

GENERICS“0 TO 0”

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▸ A Comparative Study of Language Support for Generic Programming (R Gracia 2003)

▸ An Extended Comparative Study of Language Support for Generic Programming (R Gracia 2007)

AGENDA

▸ Refine Queue

▸ Concepts/Protocols

▸ Common errors and why?

▸ Protocol Oriented Programming (IF⏲ )

▸ Finale: Swift vs Haskell in Generics

INTRODUCTION

GENERICS

▸ Grouping of similar functionality into a single Thing

▸ Parametric Polymorphism [not Just polymorphism]

▸ Compile Time / Static Polymorphism

QUEUE

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QUEUE FOR INT

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QUEUE FOR STRING

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QUEUE FOR CGPOINT

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1000’S OF THESE

▸ Cant be extended

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WHAT IS CHANGING

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IDEA 1

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ANALYSE

▸ all value semantics conform to Any Protocol by default

▸ Is it Generic?

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.

▸ NOT GENERIC

▸ Type Erasure Model

▸ Heterogeneous set capable

▸ Objectie-C NSArray is somehow similar to this

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IDEA 2:

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▸ Generic

▸ Type Safe

▸ Homogeneous set capable

▸ T==> type deduction from call site

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SO WHAT??

▸ Reduces redundancy

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SO WHAT??

▸ Type Safety

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1-….

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SO WHAT??

▸ Capability can be extended beyond the authors intention

▸ Originates from Set theory. Highly useful for FPs.

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SO WHAT FOR US????

▸ Swift uses Generics all over the Standard Library

▸ Swift has a great support for Generics

▸ Generics are awesome when all the <> brackets and T: U: make sense

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OOOH

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ADD!!

TYPELESS GENERICS

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PROPER TYPED GENERICS

+ is not defined on all types: unfortunately!!!

+

CONCEPTS

▸ + means lhs and rhs can be added. It is a concept.

▸ In C++ are just documented. No language support.

YUK

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CONCEPT == PROTOCOL

▸ Protocol to our rescue.

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SO……

▸ Expressive

▸ No Lies to the compiler

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FULL PICTURE

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FULL PICTURE

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FULL PICTURE

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AT CALL SITE

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HOW IT COMPILES?

▸ during compile time a concrete function is created in place of generic function. This is Separate Compilation.

▸ LLVM is smarter than this.

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TYPES

▸ A grouping of data structure

▸ Int, String, NavigationBarAppereance, classes.

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TYPES

▸ Protocols that are complete by themselves are proper types

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WHAT ARE NOT TYPES?

▸ Items that can not completely defined in isolation

▸ Don’t know what is the type of Self until conformed by some concrete Type

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WHAT ARE NOT TYPES?

▸ Items that can not completely defined in isolation

▸ Element is unknown unless conformed by somebody

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SO..

▸ They are Generic placeholders (Incomplete Types)

▸ so is Array,

▸ But not Array<Int>. Its a complete Type.

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THUS

▸ Protocols with Self requirement or associatedType requirement are not complete by themselves

▸ Thus, they cant be used like a Type

▸ They can be used to constrain other Types

▸ Examples:

▸ Queue<T>

▸ Array<T>

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2. TYPE CONSTRAINTS

Reduce function over a Collection Type only when the elements are SignedInteger

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NOTE:

▸ Make note that Swift provided “T:Comparable” which specifies T can be anything that conforms to a concept/protocol Comparable. Whereas, T == Int would mean T must be a Integer type.

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GENERICS VS LOOKS GENERICS

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TYPE ERASURE MODEL

▸ Generic Placeholder gives Type safety and feedback on code analysis

▸ Concrete Type parameter casts the provided argument into the Type method accepts. Hence, losing Type information. Type Erasure Polymorphism model or Not So Swift Model

CODE

CODE

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ARRAY OF PROTOCOL

▸ Array of Concrete Type cannot be implicitly converted to Array of Another Type

▸ But a single Concrete Type can be converted to

CODE

▸ Protocol are a special construct which occupies 40 bytes

▸ Int are 8 bytes on 64 bit machine

▸ Array<Int> == Array<8byte contagious memory>

▸ Array<AType> == Array<40Byte contagious memory>

▸ Swift wont transform :=> performance, memory, type loss

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WHY?

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MIXIN, DEFAULT IMPLEMENTATION

▸ DEMO

▸ Protocol Oriented Programming

▸ Avoid Subclassing

▸ Careful about: Static vs Dynamic Dispatch!!!!

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AT THE CALL SITE

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AT CALL SITE

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ANOTHER CLASS

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WHAT WE GOT!

▸ Protocol Oriented Programming

▸ We can subclass only from 1 parent. This makes multiple inheritance easy without actually inheriting

▸ Retroactive modeling (WHAT)

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RETROATTIVE MODELING

▸ Ability to add functionality after the Type has been defined completely.

▸ Even though Array is made by Swift Team we were able to extend it with useful function after 2 years finally.

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GENERICS SUPPORT FOR SWIFT

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Great Support For Generics

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ANY QUESTION?

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REFERENCES

▸ Programming". http://www.osl.iu.edu/publications/prints/2005/garcia05:_extended_comparing05.pdf. N.p., 2016. Web. 22 May 2016.

▸ "Generics In Swift, Part 2 · Episteme And Techne". Austinzheng.com. N.p., 2015. Web. 23 May 2016.

▸ Cook, Nate. "Are Swift Generics Separately Compiled?". Stackoverflow.com. N.p., 2016. Web. 24 May 2016.

▸ "Mixin". Wikipedia. N.p., 2016. Web. 24 May 2016.

▸ Tsai, Michael. "Michael Tsai - Blog - How Swift Implements Generics". Mjtsai.com. N.p., 2016. Web. 24 May 2016.